A variety of diseases exists that require regular treatment by injection of a medicament. Such injection can be performed by using injection devices, which are applied either by medical personnel or by patients themselves. As an example, type-1 and type-2 diabetes can be treated by patients themselves by injection of insulin doses, for example once or several times per day. For instance, a pre-filled disposable insulin pen can be used as an injection device. Alternatively, a re-usable pen may be used. A re-usable pen allows replacement of an empty medicament cartridge by a new one. Either pen may come with a set of one-way needles that are replaced before each use. The insulin dose to be injected can then for instance be manually selected at the insulin pen by turning a dosage knob and observing the actual dose from a dose window or display of the insulin pen. The dose is then injected by inserting the needle into a suited skin portion and pressing an injection button of the insulin pen. To be able to monitor insulin injection, for instance to prevent false handling of the insulin pen or to keep track of the doses already applied, it is desirable to measure information related to a condition and/or use of the injection device, such as for instance information on the injected insulin type and dose. In this respect, WO 2009/024562 discloses a medical device with a value sensor. A Radio Frequency Identification (RFID) unit comprises a value sensor such as a pressure sensor and is integrated with a liquid medicament container to enable wireless pressure or other medicament relevant parameter value monitoring. The liquid medicament container is coupled with a first housing part of the medical device, which first housing part may for instance constitute a pre-filled disposable injection device. The RFID unit communicates wirelessly with a control circuit that is contained in a second housing part of the medical device that is releasably attached to the first housing part. The control circuit is adapted to process the values measured by the RFID unit, to compare it with pre-defined values and to provide an alert to the user if the measured values fall outside normal operating conditions, and to communicate data relating to the measured values to an external device for further data processing.
The control circuit of the medical device described in WO 2009/024562 can thus be used with a series of pre-filled disposable injection devices, but the requirement that the RFID unit with the value sensor is contained in the medicament container of the pre-filled disposable injection devices significantly increases the costs of the pre-filled disposable injection device.
It has been described, for instance in WO 2011/117212 to provide a supplementary device comprising a mating unit for releasably attaching the device to an injection device. The device includes a camera and is configured to perform optical character recognition (OCR) on captured images visible through a dosage window of the injection pen, thereby to determine a dose of medicament that has been dialed into the injection device.